As it is well known, communication of information though radio is made using radio spectrums. Radio spectrums are in fact ranges of frequencies. Due to the limited available range of frequencies, different wireless transmission services are assigned specific ranges of frequencies which vary from one service to another. Therefore a specific wireless service can only use the spectrum assigned thereto. The limited availability of the frequency ranges on the one hand, and the increasingly growing demand for use of wireless transmission, on the other, give rise to the need of optimizing the use of the spectrum as much possible.
In certain communication networks, the communication is partly wireless and partly wireline. An example of this situation is where a wireline communication data flow such as for example one in an ISDN is subsequently to be transmitted through the air for example by microwave transmission. In such a scenario, at a certain point of the network, the wireline (physical) equipment interfaces, in any convenient manner, with the wireless (radio) equipment.
In the following, the terms “line interface” are used to refer to any baseband interface used for the wireline communication part, such as for example:    Plesiochronous Digital Hierarchy, or PDH (ITU-T: G.703)    Integrated Services Digital Network, or ISDN (ITU-T: G 703, G704, I412 and ETS300233)    Synchronous Digital Hierarchy, or SDH (ITU-T: G 703, G707, G708, G783, G784, G957, G750)    Low speed data interface (ITU-T: V.11, V.24, V28) or    Ethernet data interface (IEEE 802.3 ecc)
When a line interface is coupled to a radio equipment for transmitting data on the air, the line interface data is carried over radio channels under certain restrictions. For instance, in a typical case of a system carrying two line interfaces STM1, to be carried over two 28 MHz radio channels using two transceivers with a modulation scheme of 128QAM, it is common practice that the first STM1 is carried over the first radio channel and the second STM1 is carried over the second radio channel. Therefore the line interface is carried as a whole over one channel or, if the size of the channel would allow, several line interfaces are carried over the same channel. However such a solution presents an important drawback in view of the use of radio resources because in many occasions it may occur that by carrying the traffic of one or more line interfaces over one channel, the effective capacity of the channel to be used for carrying useful information (traffic) is not used in an optimum manner. Therefore, by using the known solutions the available resources of the radio spectrum are not flexibly and efficiently used.